This invention relates to the disposal of flammable gases by flaring.
Large quantities of unwanted flammable gas can be burnt quickly at flares of open pipe type. The gas may be supplied to such a flare at high pressure and released at high velocity, possibly sonic velocity, and one problem which arises, especially above about half sonic velocity, is that the flame can lift off the tip of the flare, so that ignition of the gas occurs at some distance from the tip of the flare. Whilst lift off is not in itself a problem, indeed, a lifted flame benefits from improved aeration, there is the possibility that the flame may be unstable and lift off to the extent that the flame is blown out, which leads to the dangerous accumulation of unburnt flammable gas. Flares may be fitted with pilot burners or flame retention devices in an attempt to maintain ignition at lift off, the former of which provide a small stable flame supplied with fuel gas from an independent source, and the latter of which operate by establishing regions of low gas velocity at the flare tip and small stable flames, which provide a continuous re-ignition source for the main flame at the flare tip if it tends to lift off the tip. However, at high gas velocities, and particularly those of or approaching sonic velocity such small flames are not sufficient for reliable flame retention and cannot provide continuity of ignition of the main flame if it is lifted to any great extent. It is an advantage if the flare can be operated with a gas velocity of the sonic order, since, inter alia, lower radiation of energy from the flame can be achieved.